Re: Compiling a project with '-ansi'

[Niccolo Medici <niccolomedici@...>]

On 9/1/16, Sam Putman <atmanistan@gmail.com> wrote:
> On Wed, Aug 31, 2016 at 9:29 AM, Niccolo Medici <niccolomedici@gmail.com>
> wrote:
>
>> In a project I'm writing I want to ensure my C code doesn't use
>> newfangled features, so I compile it with `-ansi` (or `-std=c90`). I'm
>> using gcc.
>>
>> However, in this mode the compiler emits an error:
>>
>>     /usr/include/lua5.3/luaconf.h:573:2:
>>     error: #error "Compiler does not support 'long long'. Use option
>> '-DLUA_32BITS'
>>     or '-DLUA_C89_NUMBERS' (see file 'luaconf.h' for details)"
>>
>> What should I do?
>>
>
> One possibility is to use, instead of -ansi, the flag -Wc90-c99-compat
>
> This will issue warnings rather than errors for newfangledness.

Thanks for the advise!

I ended up using "-Wc90-c99-compat -Wno-long-long".

Here are my findings:

0. The problem pertains to Lua 5.3 only. (Earlier ones don't support
integers, so the "long long" issue doesn't exist there, IIUC.)

1. We can't use -ansi (or -std=c90) because this eventually triggers
the #error line in 'luaconf.h'. At least in the stock Lua package that
comes with Ubuntu.

2. So instead we have to use warnings: -Wc90-c99-compat.

2.a. Unfortunately, while the -Wc90-c99-compat switch exists in gcc, I
don't know of equivalent clang switch.

3. We also need to add -Wno-long-long so that the Lua headers work.